1. Field of the Invention
The present invention generally relates to a data transmission apparatus and a method of initializing a remaining amount of an available bandwidth in such data transmission apparatus. More particularly, this invention relates to a data transmission apparatus comprising a first transmission unit having a first available bandwidth and a second transmission unit connected to the first transmission unit and which has a second available bandwidth smaller than the first available bandwidth and wherein an apparent available bandwidth of the whole transmission unit may be increased by setting the remaining amount of the first available bandwidth to a value equal to or smaller than the second available bandwidth.
2. Description of the Related Art
Heretofore, IEEE1394 has received a remarkable attention as a data transmission system suitable for multimedia use such as to connect home electronic equipment such as digital video recorders and to connect these electronic equipment and a computer together.
This IEEE1394 has two kinds of data transfer functions of asynchronous transfer function and isochronous transfer function. According to the asynchronous transfer function, asynchronous communication of data is effected in the memory mapped I/O system. On the other hand, according to the isochronous transfer function, data communication is effected by using channel numbers previously set on the transmission side and the reception side, and the isochronous communication of data is effected at the unit of 125 xcexcs.
The IEEE1394 is the high-speed data transmission system and is also the standard corresponding to data transfer of 100 Mbps, 200 Mbps and 400 Mbps with respect to cable medium. Therefore, all equipment based on the IEEE1394 cable environment have to assure data transfer rate higher than 100 Mbps.
When communication environments of communication equipment using infrared communication, radio communication or public communication network such as telephone line are considered, there exists an environment under which it is difficult to realize a data transfer rate higher than 100 Mbps. Heretofore, due to the above-mentioned limit of the available bandwidth, communication equipment whose available bandwidth is less than 100 Mbps could not be regarded as the IEEE1394 equipment.
Moreover, since the data transfer rate supported by the IEEE1394 is discrete like 100 Mbps, 200 Mbps, 400 Mbps, in the case of communication equipment whose data transfer rate, for example, is 140 Mbps, such communication equipment is treated as communication equipment whose available bandwidth is 100 Mbps although it has the available bandwidth higher than 100 Mbps. As a result, the available bandwidth of 40 Mbps becomes useless. Similarly, in the case of communication equipment having a data transfer rate of 300 Mbps, for example, such communication equipment is treated as communication equipment having an available bandwidth of 200 Mbps with the result that an available bandwidth of 100 Mbps becomes useless.
Therefore, it is an object of the present invention to provide a data transmission apparatus in which communication equipment whose available bandwidth, for example, is less than 100 Mbps may be regarded as IEEE1394 communication equipment and in which a useless bandwidth of communication equipment may be removed.
It is another object of the present invention to provide a method of initializing a remaining amount of an available bandwidth in a data transmission apparatus.
According to an aspect of the present invention, there is provided a data transmission apparatus which is comprised of a first transmission unit having a first available bandwidth and a second transmission unit connected to the first transmission unit and which has a second available bandwidth smaller than the first available bandwidth, wherein the first transmission unit includes a remaining amount setting means for setting a remaining amount of an available bandwidth and the remaining amount setting means sets the remaining amount of the available bandwidth to a value equal to or smaller than the second available bandwidth when the first transmission unit is initialized.
According to another aspect of the present invention, there is provided a method of initializing a remaining amount of an available bandwidth in a data transmission apparatus including a first transmission unit having a first available bandwidth and a second transmission unit connected to the first transmission unit and which has a second available bandwidth smaller than the first available bandwidth. This method of initializing a remaining amount of an available bandwidth includes a step of writing a value equal to or smaller than the second bandwidth in a memory unit which sets a remaining amount of an available bandwidth of the first transmission unit when the first transmission unit is initialized.
In the present invention, the first transmission unit has the first bandwidth. The second transmission unit is connected to the first transmission unit and has the second bandwidth smaller than the first bandwidth. For example, the first bandwidth is a bandwidth which may be used in a synchronous communication at the first transmission unit. The second bandwidth is a bandwidth which may be used in the isochronous communication at the second transmission unit. The first transmission unit is a portal comprising a bridge which connects two buses (e.g. IEEE1394 buses), and the second transmission unit is a radio transmission line interposed between two portals comprising the bridge. The first transmission unit is a bus (e.g. IEEE1394 bus), and the second transmission unit is a radio transmission line interposed between two portals comprising a bridge connected to the bus.
In the first transmission unit, the remaining amount of the available bandwidth is set to a value equal to or smaller than the second bandwidth when the first transmission unit is initialized. For example, the first transmission unit includes the memory unit for setting the remaining amount of the available bandwidth. When the first transmission unit is initialized, the value equal to or smaller than the second bandwidth is written in the memory unit.
As described above, when the first transmission unit is initialized, since the remaining amount of the available bandwidth is set to the value equal to or smaller than the second bandwidth, it becomes possible to increase the whole bandwidth apparently. Thus, communication equipment having a data transfer rate of 40 Mbps, for example, maybe apparently operated as IEEE1394 communication equipment having a bandwidth of 100 Mbps. Moreover, communication equipment having a data transfer rate of 140 Mbps, for example, can be apparently operated as IEEE1394 communication equipment having a bandwidth of 200 Mbps. As a result, it becomes possible to remove a useless bandwidth of 40 Mbps.